The brassinosteroids are a unique class of biologically active natural products that possess plant steroidal hormone activity. Their low effective concentrations for use on crops make them environmentally safe and those brassinosteroids used on a large scale are generally non-toxic. At the physiological level, brassinosteroids elicit many changes and could represent a new class of hormones in plants. The economic aspects of the brassinosteroids may have worldwide effects. For example, the brassinosteroids can be used as plant protectants from both pesticide and environmental adversity. In addition, brassinosteroids appear to be useful for insect control. Further, brassinosteroids may regulate some stage of the reproductive cycle in plants, thereby providing the means to increase or decrease the reproductive process. For example, in certain horticultural crops, it may be desirable to eliminate the flowering process to ensure continuous production of other tissues such as leaves, bulbs and other storage organs. This modulation of the reproductive process could be important in the control of certain seed bearing weeds, where cessation of the flowering cycle eliminates future generations. Brassinosteroids also appear to stimulate root growth, and external application causes no deformity of plants.
Brassinosteroids qualify for classification as biochemical pesticides. Such pesticides are generally distinguished from conventional chemical pesticides by their unique modes of action, low effective concentration, target species, and specificity. Historically, the brassinosteroids have not been used in actual agricultural applications due to the expense involved in producing them as well as the difficulty in purifying them.
It is known that once hormones, such as glucocorticoid, enter a cell, they bind to specific receptor proteins, thereby creating a ligand/receptor complex. The binding of the hormone to the receptor is believed to initiate an allosteric alteration of the receptor protein. As a result, it is believed that the ligand/receptor complex is capable of binding with high affinity to certain specific sites on the chromatin nucleic acid. Such sites, which are known as response elements, modulate expression of nearby target gene promoters.
Recent evidence indicates that in addition to intracellular, genomic effects, steroids also exhibit non-genomic effects, i.e., they affect the surface of cells and alter ion permeability, as well as release of neurohormones and neurotransmitters. Steroids such as estrogens and adrenal steroids and their naturally produced and synthetic analogs have shown membrane effects. In view of the foregoing, it appears that steroids may cause synergistic interactions between non-genomic and genomic responses resulting in alterations in neural activity or certain aspects of oocyte and spermatozoa maturation, for example.